Alkenes reaction with hydrogen sulfide

Acid-Gatalyzed Synthesis. The acid-catalysed reaction of alkenes with hydrogen sulfide to prepare thiols can be accompHshed using a strong acid (sulfuric or phosphoric acid) catalyst. Thiols can also be prepared continuously over a variety of soHd acid catalysts, such as seoHtes, sulfonic acid-containing resin catalysts, or aluminas (22). The continuous process is utilised commercially to manufacture the more important thiols (23,24). The acid-catalysed reaction is commonly classed as a Markownikoff addition. Examples of two important industrial processes are 2-methyl-2-propanethiol and 2-propanethiol, given in equations 1 and 2, respectively. 

The intramolecular addition of thiols to alkenes provides a novel entry into heterocycles. One example of this is the reaction of hydrogen sulfide with various nonconjugated dienes to form six-membered rings (equation 302).549 550... 

Reaction of an alkene with ozone leads to a 1,2,3-trioxolane, which rearranges to a 1,2,4-trioxolane (an ozonide). Subsequent treatment with hydrogen peroxide or with dimethyl sulfide leads to an aldehyde, ketone, or carboxylic acid product. When an ozonide contains a C-H unit, oxidation with hydrogen peroxide leads to a carboxylic acid, but reaction with dimethyl sulfide leads to an aldehyde 51, 52, 53, 54, 78,82,83,117. 

Sulfide groups can also be introduced by this methodology (entry 24) [405]. Simpkins and coworkers found that the reaction of acceptor-substituted alkenes 363 with diphenyl disulfide in the presence of 10 mol% of Co(eobe)2 344 and PhSiH3 as the stoichiometric hydrogen source furnished 31-71% of a-(phenylthio) carbonyl compounds 364. The intermediacy of radicals was proven by a 5-exo cyclization occurring in competition to the SH2 reaction at sulfur. 

Reaction of a four-carbon unit with sulfur sources such as hydrogen sulfide, carbon disulfide, and elemental sulfur is one of the traditional thiophene syntheses that belong to this category (Equation 18). A wide variety of hydrocarbons, for example, alkanes, alkenes, dienes, alkynes, and diynes, serve as four-carbon units. Another practical method is the sulfuration of 1,4-dicarbonyl compounds (Paal synthesis). The method has become very popular with development of sulfuration reagents such as Lawesson s reagent. The reaction of a,/3-unsaturated nitriles with elemental sulfur in basic media, Gewald synthesis, is also useful for the preparation of 2-aminothiophenes which are important compounds in dyestuff and pharmaceutical industries. 

The reaction of dimethylformamide diethyl acetal with the carbanion which forms when the isocyanide (31) is metalated gives an alkene (32) which reacts with methyl iodide to give an imidazole product (79LA1444). In the presence of base, 2-isocyanoalkane nitriles (33) react with alcohols, thiols or hydrogen sulfide to form imidazoles which have an oxygen or sulfur substituent at C-5 (Scheme 16) (79LA1602). 

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